If new intermediate classes crop up then there would be no point in fixing<br>
<br>
class (Applicative m) =&gt; Monad m where<br>
<br>
since it would have to be changed if new intermediate classes are found.<br></blockquote><div><br></div></div><div>You might check out a few articles regarding Kleisli arrows [1][2] for possibilities that live between applicative and monad. </div>

<div><br></div><div>Applicative itself is also a little on the strong side. I had to reject Applicative for one model of signal transformers because &#39;pure&#39; was not a legal constructor, even though &#39;fmap . const&#39; and &#39;&lt;*&gt;&#39; were okay. And even Functor is too strong if you want effective linearity. I&#39;ve found Adam Megacz&#39;s Generalized Arrows [3] to be a suitable chassis for weaker models. </div>